The goal of the subjective test with the subject in position A (sweet spot) was to assess whether the described playback of stereo signals over multiple loudspeakers matches the quality of stereo playback when the listener is located in the sweet spot. On average the subjects preferred the described playback scheme over stereo in the sweet spot.
To show the benefit of listening when the listener is not located in the sweet spot, the subjective test with the listening position B was carried out. As expected, the relative performance of the described scheme is better for off-sweet-spot listening since it maintains the extent of the virtual sound stage.
Only informally tested, the described playback scheme results in a virtual sound stage which hardly depends on the listener's position. The listener can move and the stage and instruments remain at their (absolute) spatial position. This is in contrast to wavefield synthesis systems when they are used for stereo playback. Usually, the left and right stereo signals are emitted as plane waves in such systems, resulting in that the virtual stage moves as the listener moves. The scheme described gives the flexibility of playing back stereo signals over wavefield synthesis systems where the distance of each virtual source (signal) can be freely determined. Previously, a large sweet spot could only be obtained by emitting plane waves, i.e. by mimicking a sound stage infinitely far away.